The present invention relates to an apparatus for applying a torque to a drilling tubular in an earth drilling machine, and in particular to an apparatus for applying a torque to casing.
After a bore hole has been drilled in an earth formation, it is conventional in many applications to line the bore hole with a large diameter casing. Such casing is typically provided with threads at each end, and adjacent lengths of casing are threaded together to form a string of casing which is lowered into the bore hole. In assembling the string of casing it is necessary to apply a pre-determined torque to adjacent lengths of casing in order to make up the threaded joints properly.
In the past, hydraulic chain tongs such as Model CH-20 of Weatherford Company have been used to make up threaded joints on large diameter casing. Such chain tongs grip the exterior of the casing to apply the desired torque. Though suitable for many applications, such hydraulic chain tongs suffer from severe disadvantages that make them inappropriate for certain applications. Hydraulic chain tongs for large diameter casing are unacceptably large, heavy, slow, and expensive for the use with modern top head drive drilling machines of the type that provide limited space on the drilling floor around the string.
U.S. Pat. No. 3,747,675 to Brown discloses another rotary drive connection for casing drilling string. This drive connection is intended to interconnect a rotary swivel with a string of casing in a drilling operation, and it includes internal slips for lifting the string, elements for gripping the interior of the casing to rotate the string, and a sliding seal for sealing off the interior of the string. In that the seal engages the interior side wall of the casing, it does not utilize the threaded end of the casing to prevent drilling fluid from escaping from the casing. In many cases, the interior side wall is not sufficiently smooth or round to create an effective sealing surface. Furthermore, the internal gripping elements are designed to lock when the drive connection is rotated in a right hand sense, and no means are provided for selectively releasing the internal gripping elements while the drive connection is being rotated in a right hand sense. For these reasons, the sealing potential of the threaded upper end of the casing (which is machined to act as an excellent sealing surface) is not used and the associated advantages are lost.
The present invention is directed to an improved apparatus for applying torque to a drilling tubular such as a large diameter casing, which overcomes the disadvantages described above.